What I tried with my tank was mixing boiled linseed oil and paint thinner 40:60, and rub it into the tank (clean tank). I found this info from a guy who had experience as a paint scientist so to say. After a few days of dabbing and rubbing youll find that it adds to the original color, kind of brings it out. I dont know if your tank is supposed to be white or yellow, but its something that could help.
The outgassing from the fuel thru the tank will cause bubbles to form in the paint, some of which can be pretty big. My brother painted a tank on his RM last summer with Krylon Fusion paint and by this spring there were quite a few bubbles.
Actually no, if u use the proper paint, (ppg makes a good one), u will have no problems. See your local hot rod paint-supplier...i say hot rod b/c those type suppliers usually carry the "odd" type paints. i forget the number that u need, but a quality shop will know.
HOWEVER, that plastic renew does indeed work, but its directions must be followed exactly, meaning it is labor-intensive...my stuff usually looks ~85% as good as new...
I use a trickling water-hose and electric hand-sander (air sanders usually are too uncontrollable, making you get the plastic too hot, which will melt it---SUCKS...).
If you can befriend a local hot rod shop, they can be cajoled into blasting your tank with baking-soda, which will save tons of time.